Injection blow molding processes and apparatus are widely known and widely used in industry. For example, reference should be had to U.S. Pat. No. 3,183,552 to Farkas, U.S. Pat. No. 3,819,314 to Marcus, U.S. Pat. No. 3,339,231 to Piotrowski and Canadian Pat. No. 995,418 to Cannon et al.
It is and has been a long standing objective of art processes to achieve a high productivity, i.e., to develop a process with a rapid, efficient and economical operating cycle. Art processes known heretofore are subject to one or more significant disadvantages. Frequently, they are cumbersome and expensive to operate, and characterized by a relatively slow operating cycle. A shorter operating cycle is particularly desirable since it is directly translatable into a larger number of end products produced.
Processes are known with overlapping cycles in order to reduce overall cycle time, for example, by providing that while one parison is being molded another is being blown and still another is being removed. However, even with processes using overlapping cycles the output still leaves much to be desired even after improvement in cycle time.
The foregoing difficulties are at times further compounded by lack of reliability of prior art processes necessitating interruptions of the operation that impair operating efficiency.
Stack-molds are frequently used for injection molding of relatively flat articles and also of cup-shaped articles. The principle of such a mold is to use back-to-back injection molds in order to double the output of the unit without substantially increasing its size. Thus, if a stack-mold is used for a two impression mold one would obtain four impressions consisting of a "stack" of two times two impressions, back-to-back.
However, difficulties are encountered in using stack-molds in injection blow molding since doing so affects other components of the mold set besides the injection mold. For example, a preferred operation embodied in copending U.S. patent application Ser. No. 618,956, for INJECTION BLOW MOLDING PROCESS AND APPARATUS, By Tommy Thomas and John W. West, filed June 11, 1984, now U.S. Pat. No. 4,540,543, issued Sept. 10, 1985, assigned to a common assignee and the disclosure of which is incorporated herein by reference, shows, in addition to the injection mold, a blow core, a blow mold, a removal mold and a removal mandrel. When one stacks this injection mold in this type of assembly insufficient space is provided for the removal of finished parts without extraordinary measures and casing interference of the function of one removal mold with that of the other.
Accordingly, it is a principal object of the present invention to provide a process and apparatus for injection blow molding hollow plastic articles using a stack-mold for injection, and to provide a mold assembly characterized by a rapid, efficient and economical operating cycle in which finished parts removal may be effected without interference.
It is a still further object of the present invention to provide a process and apparatus as aforesaid which is convenient and easy to use on a commercial scale and may be reliably used with high productivity.
Further objects and advantages of the present invention will appear from the following specification.